Fuse circuits can be used in a variety of semiconductor applications, e.g., memory devices or programmable logic devices. For example, memory devices can include fuse circuits for providing fuse data. FIG. 1 illustrates a block diagram of a conventional fuse circuit 100.
In FIG. 1, a transistor 104, e.g., a PMOS transistor, is coupled to a node of a fuse 102 for providing a blowing current IB to the fuse 102 in response to a trimming signal. The trimming signal can be input to a gate of the transistor 104 via inverters 110 and 112. A power supply can be connected to a source of the transistor 104 for providing an input voltage VDD to the transistor 104. Another node of the fuse 102 is connected to ground. A transistor 106, e.g., a PMOS transistor, is coupled to the fuse 102 for providing a reading current IR (IR<IB) to the fuse 102. A bias voltage VB can be provided to a gate of the transistor 106. The power supply can be connected to a source of the transistor 106 for providing the input voltage VDD to the transistor 106. Furthermore, an inverter 108 is coupled to the fuse 102 to detect a voltage drop across the fuse 102 and output a signal according to the voltage drop.
The fuse 102 has an intact state and a blown state. If the fuse 102 is blown, resistance of the fuse 102 can be relatively high, e.g., 100KΩ. Otherwise, the resistance of the fuse 102 can be relatively low, e.g., 100Ω. That is, the fuse 102 exhibits a highly resistive condition or a short circuit condition. If the trimming signal is asserted, the transistor 104 can be turned on to enable the blowing current IB to flow through the fuse 102 to blow the fuse 102. In order to detect whether the fuse 102 is in the blown state or in the intact state, the transistor 106 can provide the current IR flowing through the fuse 102. The inverter 108 can generate a signal indicative of the states of the fuse 102 according to the voltage drop across the fuse 102. If the voltage drop across the fuse 102 is lower than a predetermined level VTHR, e.g., 1V, the fuse 102 can be determined in the intact state. The inverter 108 can provide a logic high signal at OUT. If the voltage drop across the fuse 102 is higher than the predetermined level VTHR, the fuse 102 can be determined in the blown state. The inverter 108 can provide a logic low signal at OUT.
However, the fuse 102 may be heated or even melt by an electrostatic discharge current flowing through the fuse 102. The electrostatic discharge current can be a sudden and momentary electric current that flows between two nodes at different electrical potentials when an electrostatic discharge event occurs. Electrostatic discharge events can be caused by static electricity. The static electricity can be generated through tribocharging, in which certain materials become electrically charged after they come into contact with another different material and are then separated. For example, the friction between two fuse circuits may result in tribocharging, thus creating different electrical potentials across the fuse. As a result, an electrostatic discharge current can flow through the fuse. As such, the fuse may be permanently damaged, which may cause detection errors of the states of the fuse.
Additionally, the resistance of the fuse 102 may vary because of process degradation, ambient temperature change, variation of supply voltage or fuse aging. The resistance of a blown fuse may decrease, such that the voltage drop across the fuse may decrease lower than the predetermined level VTHR, which result in a logic high signal at OUT. As such, inconsistent detection results of the fuse circuit may cause errors and decrease system robustness.